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Ca3Co4O9+δ (CCO) cathode has been extensively studied for its excellent thermal expansion matching with commonly used electrolytes. CCO composite cathode with different concentrations of La0.9Sr0.1Ga0.8Mg0.2O3 (LSGM) was prepared to evaluate its performance on LSGM electrolyte in this work. The appropriate amount of LaCoO3 generated by the in-situ reaction of CCO and LSGM under operating conditions significantly enhances the oxygen exchange ability of CCO cathodes. The composite cathode containing 60 wt. % CCO and 40 wt. % LSGM (C-LGM60) exhibits the best electrochemical performance and the lowest polarization impedance among the C-LGM series cathodes. The area-specific resistance (ASR) of C-LGM60 is 0.06 Ωcm2 at 750 °C. The maximal power density of the electrolyte-supported cell with C-LGM60 cathode reaches 489 mWcm-2 at 800 °C. After a 10 h stabilizing, there is no observable decline of the cell during the next 40 h of discharge. These results encourage the research of using CCO cathode on LSGM electrolytes and make valuable improvements on the development of SOFC cathode. [ABSTRACT FROM AUTHOR]

Solid oxide fuel cell (SOFC) is regarded as an environmentally friendly energy conversion device, which can directly convert the chemical energy stored in the fuel to the electrical energy. However, the degradation of cathodes caused by Cr‐containing steel interconnects is a major problem that limits the broader application of SOFC. Herein, a novel A‐site high entropy oxide, based on the cobalt‐free PrBaFe2O5+δ (PBF) cathode, La0.2Pr0.2Nd0.2Sm0.2Gd0.2BaFe2O5+δ (LPNSGBF), is proposed as a high catalyst activity and Cr‐tolerance cathode for SOFC. The anode‐supported cell with the LPNSGBF cathode exhibits an excellent peak power density of 1020.69 mW cm−2 at 800 °C, which is better than that of the PBF (794.96 mW cm−2). Moreover, under the Cr‐containing atmosphere, the outstanding stability of the single cell with the LPNSGBF for 100 h with a degradation rate of 0.17% h−1, is much lower than the 0.79% h−1 for that of the PBF cathode. The study provides a new strategy for achieving the enhanced oxygen reduction reaction and high Cr‐tolerance of the cobalt‐free cathode by high entropy doping. [ABSTRACT FROM AUTHOR]

The existing Ni cermet anodes in single-chamber solid oxide fuel cells (SC-SOFCs) usually perform poorly in hydrocarbon-air mixture owing to the reduction–oxidation cycles (redox) and latent reoxidation at operating temperatures. In this study, the redox and reoxidation tolerances of Ni cermet anode, composed of Ni metal and gadolinium-doped ceria (GDC) electrolyte, are investigated and evaluated in SC-SOFC conditions. The catalytic performances, resistance properties, and microstructure evolution of the Ni cermet are measured under different CH4-O2 ratios (M) in the temperature range of 700–800 °C. Unlike the general perspective that the electrolyte materials are inactive for the catalytic reaction of fuel, GDC shows a superior catalytic activity for CH4 reforming, especially the complete oxidation. It significantly reduces the presence of O2 on Ni metal, resulting in an improvement of redox and reoxidation tolerance. The obtained results unveil a fascinating hidden side that the electrolyte materials of SC-SOFCs play an important role in the catalytic reaction of fuel and Ni-GDC is a promising anode for SC-SOFCs. [ABSTRACT FROM AUTHOR]

[Display omitted] The cathodes of solid oxide fuel cells (SOFCs) often suffer from detrimental cation segregations and associated impurities poisoning, leading to insufficient electroactivity and poor stability. Here we developed a medium-entropy double perovskite GdBa(Co 1.2 Mn 0.2 Fe 0.2 Ni 0.2 Cu 0.2)O 5-δ (ME-GBCO) for promising SOFC cathode. The increased configuration entropy can effectively tailor the surface composition with in situ formed active BaCoO 3-δ (BCO) species, rather than inert and deleterious BaO x segregation on parent GdBaCo 2 O 5-δ (GBCO) surface. Accordingly, the layered ME-GBCO cathode with beneficial surface reconstruction exhibited not only high oxygen reduction activity but excellent durability against CO 2 impurity, enabling it a very attractive cathode for intermediate temperature SOFCs (IT-SOFCs). Our study provides a new idea for development of efficient and durable cathodes via configurational entropy induced rational surface reconstruction. [ABSTRACT FROM AUTHOR]

Rare-earth site high entropy double perovskite oxides with different molar ratios have been evaluated as the cathodes for intermediate-temperature solid oxide fuel cells (IT-SOFC). The effect of configuration entropy on crystal structure, electrical conductivity, electrochemical performance and stability are investigated. Our results reveal that the activity of all high entropy oxides show enhanced electrochemical activity. Among them, the equimolar one (HEO) exhibits the highest activity with a low polarization resistance of 0.05 Ω cm2 at 700 °C. Moreover, it exhibits excellent stability in the CO 2 -containing atmosphere. The enhanced activity and operational stability can be attributed to reduced surface Ba segregation and the formation of active and robust BaCoO 3-δ nanoparticles on HEO surface, rather than BaCO 3 and Co 3 O 4 phases. This work indicates that configurational entropy engineering is very effective for rational surface composition regulation. [ABSTRACT FROM AUTHOR]

The stability of solid oxide fuel cells (SOFCs) cathodes is often severely damaged by impurity poisonings from Cr vapors. Here we report a medium entropy GdBa(Mn 0.2 Fe 0.2 Co 1.2 Ni 0.2 Cu 0.2)O 5+δ (ME-GBCO) double perovskite cathode, which exhibits remarkably improved Cr-tolerant ability. The polarization resistance (R p) of GBCO increases from ∼0.44 to ∼0.70 Ω cm2 after 20 h exposure to Cr in air at 700 °C. In contrast, R p value of ME-GBCO cathode increases from ∼0.16 to ∼0.24 Ω cm2 under the same condition. The enhanced operational stability is attributed to the in situ formed BaCoO 3-δ (BCO) nanoparticles on ME-GBCO surface, which is very inactive to Cr vapors. This work highlights that the configuration entropy modulation is an effective avenue for surface engineering and for the development of robust cathode materials for SOFCs. [ABSTRACT FROM AUTHOR]

Perovskite type SrCo 0.9 Ta 0.1 O 3-δ (SCT91) cathode exhibits high activity for oxygen reduction reactions, but the instability in Cr-containing atmosphere restricts its application in intermediate temperature solid oxide fuel cells (IT-SOFCs). In this study, a B-site medium-entropy SrCo 0.5 Fe 0.2 Ti 0.1 Ta 0.1 Nb 0.1 O 3-δ (SCFTTN52111) cathode is proposed and investigated as a potential Cr-tolerance cathode. The electrochemical activity of pristine SCT91 cathode degrades rapidly in the presence of volatile chromium species. In contrast, SCFTTN52111 performs very stable. Chromium vapors prefer to react with segregated SrO species rather than Co 3 O 4 precipitates. Significant secondary phases of SrCrO 4 and Co 3 O 4 are detected on SCT91 electrode, while only trace by-products are found on medium-entropy cathode. The better Cr tolerance is closely related to the enhanced structural stability by medium-entropy engineering and reduced surface Sr segregations. This work sheds light on the development of robust cathodes for IT-SOFCs through rational design of configuration entropy. • A SrCo 0.9 Ta 0.1 O 3-δ derived medium-entropy cathode is developed. • Cr deposition on medium-entropy cathode is studied. • Cr vapors preferentially deposit on surface Sr rather than on Co 3 O 4 segregations. • Medium-entropy cathode shows significantly enhanced Cr tolerance. [ABSTRACT FROM AUTHOR]

Perovskite type SrCo 0.9 Ta 0.1 O 3-δ (SCT10) is a promising cathode for solid oxide fuel cell (SOFC), but its stability towards Cr impurities is not yet exploited. Herein, the Cr deposition on the electrochemical performance of SCT10 cathodes is evaluated at 700 °C with a cathodic constant current density of 200 mA cm−2. Both polarization and impedance results reveal that Cr impurities lead to serious performance degradation, especially in wet condition. Significant morphology damages occur after Cr exposure and the formation of SrCrO 4 and Co 3 O 4 secondary phases on the cathode surface are determined, which greatly deteriorates the oxygen reduction kinetics and thereby the cathode activity. Our study highlights that surface Sr segregation plays a vital role for Cr deposition and special attention should be paid for the practical applications in SOFC. [Display omitted] • Cr deposition on SrCo 0.9 Ta 0.1 O 3-δ cathode is systematically studied. • Cr vapor preferentially reacts with segregated SrO rather than Co 3 O 4 species. • Cr deposition significantly deteriorates oxygen reduction kinetics. • SrCrO 4 and Co 3 O 4 secondary phases are formed on cathode surface. [ABSTRACT FROM AUTHOR]

Electrochemical performance and stability of co-synthesized Sm 0.5 Sr 0.5 CoO 3 -Sm 0.2 Ce 0.8 O 1.9 oxygen electrode (SSC-SDC) are investigated in half-cell under successive cathodic-anodic-cathodic-anodic polarizations for use in reversible solid oxide fuel cells (RSOFCs) for the first time. The results show that the coarsening and agglomeration of co-synthesized SSC-SDC electrode particles under cathodic polarization are responsible for its performance degradation. However, degraded performance caused by cathodic polarization could be compensated by the subsequent anodic polarization due to the disintegration of agglomeration, finally leading to relatively stable performance under alternate cathodic-anodic polarizations. Consequently, the electrochemical performance of co-synthesized SSC-SDC electrode can be manipulated reversibly by successive cathodic-anodic-cathodic-anodic polarization operations, indicating the co-synthesized SSC-SDC is a promising oxygen electrode candidate for RSOFCs. [ABSTRACT FROM AUTHOR]

YSZ (Y 2 O 3 -stabilized ZrO 2 )/SDC (Sm-doped CeO 2 ) bilayer electrolyte film was successfully fabricated on NiO/YSZ anode substrate using stepwise sintering processing by screen-printing technique. OCVs (open-circuit voltages) of 1.06 V, 1.05 V and 0.88 V were achieved at 750 °C for single cells with bilayer electrolyte of 12 μm-SDC/8 μm-YSZ, 12 μm-SDC/5 μm-YSZ, and 12 μm-SDC/2 μm-YSZ, respectively. Interdiffusion of ions at YSZ/SDC interface and formation of YSZ–SDC solid solution after sintering at 1400 °C for 2 h was investigated. The EDX result suggested that the region for the interdiffusion in a YSZ/SDC bilayer structure was 2.0 μm from the YSZ/SDC interface into the YSZ layer for Sm and Ce, and 0.5 μm into the SDC layer for Zr and Y. The YSZ–SDC solid solution exhibited a low electrical conductivity, which negatively affected the performance of single cell. After two thermal cycles, the maximum power density of the single cell exhibited a significant decrease. The destruction of YSZ/SDC bilayer electrolyte structure was not observed during the thermal cycles. [ABSTRACT FROM AUTHOR]

The performance and stability of the Sm 0.5 Sr 0.5 CoO 3 –Ce 0.8 Sm 0.2 O 1.9 composite with a weight ratio of 7:3 (SSC-SDC73) were studied and evaluated as oxygen electrode of high temperature solid oxide electrolysis cells (SOECs). The co-synthesized SSC-SDC73 oxygen electrode exhibited better electrochemical activity and stability than that of physically mixed one for the oxygen oxidation reaction. The effect of anodic polarization current on the co-synthesized SSC-SDC73 oxygen electrode was further investigated under the relative low and high currents at 800 °C in air, respectively. The obtained results demonstrated that co-synthesized SSC-SDC73 oxygen electrode exhibited a better stability under low anodic polarization current. While a higher anodic polarization current could promote the slight agglomerate and delamination of the electrode. Therefore, the polarization current is a key operating parameter for SSC-SDC73 oxygen electrode under the SOEC operation conditions. [ABSTRACT FROM AUTHOR]

[Display omitted] • Sr-deficient medium-entropy cathodes are developed for IT-SOFC. • A single cell with S0.95CFTTN cathode yields a PPD of 1153.5 mW cm−2 at 800 °C. • Sr segregation and Cr poisoning are effectively inhibited by introducing Sr-deficiency. In this work, Sr-deficiency is proposed as an effective strategy to improve the oxygen reduction reaction (ORR) activity and Cr tolerance of medium-entropy Sr 1-x Co 0.5 Fe 0.2 Ti 0.1 Ta 0.1 Nb 0.1 O 3-δ (S1-xCFTTN, x=0–0.15) cathodes for intermediate temperature solid oxide fuel cells (IT-SOFCs). With proper Sr-deficiency, S0.95CFTTN possesses the highest electrical conductivity and fastest oxygen exchange kinetics within tested samples. The optimized cathode yields outstanding ORR activity with a polarization resistance of 0.024 Ω cm2 at 700 °C, much lower than 0.037 Ω cm2 for SCFTTN cathode. Based on these, an anode-supported cell with S0.95CFTTN cathode exhibits a peak power density of 1153.5 mW cm−2 at 800 °C, much higher than that with SCFTTN cathode. Moreover, the S0.95CFTTN cathode displays dramatically enhanced Cr tolerance ability, which is due to the Sr-deficient diminishes surface Sr segregation and subsequent the formation of SrCrO 4. Our results indicate appropriate Sr-deficiency is an effective approach to enhance the ORR activity and stability of SOFC cathodes. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • LSFT is used as anode electrocatalyst for hydrocarbon fueled SOFC. • LSFT shows good electro-activity toward CH 4 direct oxidation. • LSFT keeps stable in H 2 fuel with different H 2 S contents up to 750 ppm for 24 h. • LSFT presents a good carbon deposition tolerance. Abstract Efficient and direct utilization of hydrocarbon fuel in a solid oxide fuel cell (SOFCs) is highly desirable. However, the carbon deposition and contaminants poisoning issue should be overcome. In this work, we developed a titanium-doped (La,Sr)FeO 3 ceramic oxide (LSFT) anode which integrates the advantage of high durability of titanate perovskite and super electrocatalytic activity of ferrite-based perovskite for methane-fueled SOFCs with H 2 S impurity. Its electrocatalytic activity and operational durability in H 2 with various H 2 S contents and humidified CH 4 fuel were systematically investigated. We found that the LSFT perovskite oxide anode showed acceptable activity and durability toward methane direct oxidation, and excellent coke and sulfur tolerance up to 750 ppm, making it a promising electrocatalyst for direct use of hydrocarbon fuels such as natural gas in high-temperature SOFCs. [ABSTRACT FROM AUTHOR]

Solid silver (Ag) is widely used current collector for solid oxide fuel cells (SOFCs). Here, its structure stability is examined in methane-oxygen mixed gas at a furnace temperature range of 600–750 °C. Rapid porosity formation is observed for solid Ag samples, especially in the presence of Ni/yttria-stabilized zirconia (YSZ) anode materials. This is mainly attributed to simultaneous diffusion of hydrogen, carbon monoxide and oxygen into Ag bulk, followed by subsequent interaction resulting in the formation of water and carbon dioxide gas. The obtained results demonstrate that partial oxidation of methane and the formation of hydrogen and carbon monoxide play an important role in the rapid porosity formation of Ag under the above specified operating conditions. Furthermore, the porosity formation of Ag samples is closely related to methane-oxygen-ratio ( R mix ) and operating temperatures. [ABSTRACT FROM AUTHOR]

The development of highly efficient and robust cathodes is crucial for intermediate temperature solid oxide fuel cells (IT-SOFC). Perovskite type SrCo 0.9 Ta 0.1 O 3-δ (SCT91) is a promising cathode but its instability against CO 2 limits the practical application. In this work, a new medium-entropy SrCo 0.5 Fe 0.2 Ti 0.1 Ta 0.1 Nb 0.1 O 3-δ (SCFTTN52111) cathode is designed and evaluated. The effect of configuration entropy on electrical conductivity, physical and electrochemical properties are studied in detail. The SCFTTN52111 cathode exhibits a lower polarization resistance of 0.033 Ω cm2 at 700 °C, superior to 0.040 Ω cm2 of SCT91 parent. The higher oxygen reduction activity is attributed to its larger surface exchange coefficient and smaller particle size. More importantly, SCFTTN52111 displays outstanding stability and high CO 2 tolerance, due to a more negative value of average metal-oxygen bond energy and significantly reduced surface Sr segregation. Our study provides a feasible and effective entropy engineering approach to design high-active and durable cathode materials for SOFCs. [Display omitted] • A medium-entropy cathode is developed for IT-SOFC. • SCFTTN52111 achieves a low polarization resistance of 0.033 Ω cm2 at 700 °C. • Greatly suppressed Sr segregation is found in medium-entropy cathode. • SCFTTN52111 shows superior resistance towards CO 2 poisoning. • Tailoring configuration entropy is a promising approach for new cathode design. [ABSTRACT FROM AUTHOR]

Surface morphology of cathode has a significant impact on the oxygen reduction reaction (ORR) activity as well as the performance of solid oxide fuel cells (SOFCs). Up to now, great efforts have been devoted to decorate the microstructure of SOFC cathode, such as changing synthesis method, infiltration, electrospinning and so on. Herein, we report an effective and feasible method to reconstruct the surface of Ca 3 Co 4 O 9+δ (CCO) cathode by reduction and re-oxidation process, during which remarkable morphology change is observed as the surface is wrinkled with the formation of numerous small particles. ORR activity of CCO cathode is notably improved after surface reconstruction, since area specific resistance (ASR) of CCO cathode significantly decreases from 0.48 Ωcm2 to 0.19 Ωcm2 at 700 °C. Specific surface area of CCO increased and calcium and cobalt oxide nanoparticles are generated after the redox treatment. The oxygen adsorption ability of the CCO is largely enhanced, which contributes to the performance promotion of CCO cathode after the redox treatment. Overall, we propose a feasible method to reconstruct CCO surface to promote the ORR activity effectively and study the corresponding mechanism thoroughly, all of which make valuable improvements on the development of SOFC cathode. [Display omitted] • Surface reconstruction is achieved by a redox treatment. • Calcium oxide and cobalt nanoparticles are formed on redox-treated CCO surface. • Re-oxidized CCO cathode shows higher ORR activity than pristine CCO cathode. [ABSTRACT FROM AUTHOR]

Electrochemical reduction of CO 2 under the high temperature electrolysis condition with favored kinetics is a promising method to utilize and convert CO 2 to valuable chemicals and to reduce its environmental impact. In this work, the electrochemical performance of perovskite-type La 0·3 Sr 0·7 Fe 0·7 Ti 0·3 O 3 (LSFT) oxide was thoroughly investigated as a cathode for high temperature solid oxide electrochemical reduction under practical CO 2 electrolysis conditions of various current densities, partial pressures, and different CO–CO 2 mixtures. The rate-limiting step of CO 2 reduction on the LSFT surface was determined by the electrochemical impedance spectroscopy technique with a three-electrode configuration. The exceptional performance of LSFT cathode is confirmed as reflected by the low polarization resistance and the extremely low activation energy. Moreover, improved electrode performance is also obtained on the reduced LSFT sample under reducing atmosphere with CO, while the rate-determining step is not changed. It is also confirmed that the reduced LSFT cathode gives increased surface oxygen vacancy concentration which is believed to serve as accommodation for chemical adsorption and consequently the active sites for electrochemical activation of CO 2 , leading to the improved electrochemical performance. • Electrochemical activity under practical CO 2 reduction condition is studied. • Cathode polarization of LSFT for CO 2 reduction is verified with 3-electrode study. • LSFT shows super-low polarization and activation energy for CO 2 reduction in SOEC. • Reduced LSFT with increased oxygen vacancies benefits the HT chemical adsorption and activation. [ABSTRACT FROM AUTHOR]